A LiteralExpression is a final expression representing a lexical
literal. As such, all LiteralExpressions are also leaf expressions.
Therefore, class literals and this literals, though called
"literal", are not here considered to be literal expressions.
Another consequence of this definition is that the value of all
LiteralExpressions can be determined at parse-time whereas the
value of class literals and this literals can only be determined at
compile-time.